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Malignant Neoplasm of Unknown Primary Site B052

Last amended 
25 June 2015
Current RMA Instruments:
Reasonable Hypothesis
80 of 2014
Balance of Probabilities
81 of 2014
Changes from Previous Instruments:

SOP Bulletin 177

ICD Coding:
  • ICD-9-CM Codes: 199
  • ICD-10-AM Codes: C80

These SOPs apply when there is a metastatic neoplasm for which the primary site cannot be determined. See comments below. If the primary site is known, code to the primary site.

Is specific evidence required to apply the SOPNo.

This diagnosis is based on histopathology identification of the presence of a malignancy, where investigation has failed to find a likely primary source.

Are there sub-factors that require specific information? – Yes.

There is a factor that applies only to a "head and neck squamous cell carcinoma of unknown primary site" (defined in the SOP).

Conditions excluded from SOP
  • Hodgkin’s lymphoma
  • Malignant melanoma
  • Metastatic neoplasm where the primary site has been identified
  • Non-Hodgkin’s lymphoma
  • Soft tissue sarcoma
Useful diagnostic investigations / evidence
  • Histopathology of any surgical or biopsy specimen.
  • CT, MRI

The RMA SOP definition says a malignant neoplasm of unknown primary site means a metastatic malignant neoplasm for which the site of origin (i.e. the primary site) cannot be identified after a complete history, physical examination and appropriate investigations have been carried out.

The extent of appropriate investigation would usually depend on the patient’s clinical condition and be decided by the treating practitioners. Seek medical advice if in doubt.